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Stardust to catch a comet by the tail

WHEN Comet Wild-2 passes within 420 million kilometres of Earth in December 2003, NASA intends to be there to meet it. Last month, the American space agency gave the go-ahead for the latest in its leaner, meaner missions for the millennium. In February 1999, the spacecraft Stardust will set off for the cloud of ice and dust that surrounds Wild-2, taking samples to bring back to Earth.

The journey to catch its interplanetary prey will take almost four years, and Stardust will have to earn its keep during that time by collecting samples of the interstellar dust that streams into our Solar System from the direction of the constellation Scorpio. If all goes to plan, it will be the first American mission to return with samples since Apollo in the 1970s. With this material scientists hope to unravel some of the mysteries surrounding the birth of the Solar System and even the origin of life.

Planetary scientists believe that the Sun and the planets formed roughly 5 billion years ago from material that may be very similar to the dust streaming into our Solar System now. The outer gaseous planets – Jupiter, Saturn, Uranus and Neptune – may have formed from cometary material. Remnants from this process, they think, are preserved as lumps of ice and rock in the outer Solar System. These objects may also have collided with the inner, rocky planets and vaporised on impact providing a significant part of their atmospheres.

With an idea of the amount and type of material in the cloud around Wild-2, astronomers may be able to work out what the early Solar System was …